1. Field of the Invention
The present invention relates generally to the field of devices for lifting ships including canal locks and mechanical lifting devices.
2. Description of the Prior Art
As an example of a common method of lifting ships, one merely has to consider the design of the Panama Canal. Today's Panama Canal operates conventional locks raising ships three steps from one ocean to a lake then lowering them three steps again to the other ocean. Typical operation of the present day locks releases about 85 thousand cubic meters (22.4 million gallons) of fresh water to the sea each to raise and then to lower a ship. Based on a Year 2003 reported average of 38 ship transits per day, about 3.23 million cubic meters (1.7 billion gallons) of fresh water were used per day that year.
During the tropical rainy season, the present Panama Canal typically receives sufficient water to permit the highest throughput of ships. Only about half the rainy season rainfall on the canal watershed is used to lift or lower ships, some is used to generate power, but much goes out to sea unused. In contrast, dry season water reserves, enhanced by occasional rains, are at times insufficient for maximum canal throughput, a limitation costly to shippers and to the Panama Canal Authority (ACP). Enhancing water storage within the canal's watershed to span longer dry seasons has been contemplated, and should be done regardless of other future canal plans.
Two other limitations of the present Panama Canal that impact both world shipping and ACP's revenues are: 1) ships larger than Panamax Class cannot transit and 2) during periodic lock overhauls canal transits are sharply reduced. A “Panamax Class” ship is the largest that physically fits inside a present day Panama Canal lock. Without the possibility to transit their larger ships at Panama, shippers resort to costlier alternatives and Panama loses that business. The impact of lock overhauls on revenues of both the shippers and Panama is self-evident.
A new set of locks for bigger ships would be financially attractive as it would allow more ships, bigger and smaller alike, to transit the Panama Canal. Also, a new set of locks would help to reduce the relative impact of periodic overhauls on transits. It must be noted, however, that it would be impossible to eliminate overhauls with any system.
Panama's decision of if and what to build depends on the required capital investment and the return on investment the improvement project will provide. The improvement project includes widening, deepening, and straightening navigation channels in addition to building new locks and dams. Naturally, lowering the cost of the improvement project and maximizing the utility of the improvements would increase the chance of the project being financially viable.
Another method of lifting ships is the counter-balance approach for simultaneously lifting and lowering floating vessels. A working example of such a mechanism can be found on the waterway between Edinburgh and Glasgow, Scotland. The Scottish device, named the Falkirk Wheel, consists of two chambers mounted on opposite ends of balance “beams” that rotate on an axis halfway between the two chambers. The chambers “hang” like pendulums on the ends of the “beams” to stay upright. Being equidistant from the axis of rotation, the chambers counter-balance each other. When chamber positions are transposed, the lifted chamber docks and seals with the upper waterway aqueduct to allow boats to enter or exit. The lowered chamber dips into the lower waterway where boats also enter or exit. The Falkirk Wheel is relatively small and lifts or lowers relatively small boats or barges a height of 35 m (115 ft). A giant Falkirk Wheel for lifting and lowering the biggest of ships is not practical. The lift disclosed herein has a distinct advantage over other ship lifts in that a pair of chambers, connected to each other with a large number of beams, are always on the ground. Major equipment failure may stall translation of the chambers, but structural collapse is highly unlikely.
Given the configuration and lift height of the Falkirk Wheel, it is not feasible to greatly increase the dimensions of the chamber to handle much larger vessels. Geometry alone will limit how much a Falkirk Wheel chamber can be enlarged to fit larger vessels for a given lift height. From the perspective of geometry alone, if the lift were higher then the maximum vessel could be larger whereas if the lift were lower the maximum vessel would be smaller. There are structural and material limitations to contend with when changing dimensions. Further, the Falkirk Wheel may not be practical when considering the tide range at the Panama Canal.
Disclosed herein is the Shelton Ship Lift (SSL) that requires capital investment comparable to the favored concept of the Panama Canal Authority (ACP) yet it can yield improved return on investment. Potential benefits include: 1)costly watershed enlargement is not necessary to meet the modest water/power needs for SSL operation; 2) the SSL can transit as many ships per day as the single lane concept presently being considered by Panama, but uses less than half the water/power; and, 3) a stretched version of the SSL to raise/lower multiple ships can increase ship throughput.
By using the SSL, excess canal watershed water can be made available for other uses, such as for the generation of hydroelectric power, for crop irrigation, or for drinking.